Are your measurements from instruments, or simulated? Are the regularly spaced? Share a few rows of your sample data.
If your data is slow / sparse, then you need to find the two nearest times and the current time position between them, then interpollate the speeds, as @Chrisir
If you data is fast / thick, then it is probably good enough to simply display the most timely single measurement. You can keep the current row id in a global variable and march up to the next row each time with a while() loop.